1. Field of the Invention
The invention is related generally to nuclear reactors and in particular to radiation shields for space nuclear reactors.
2. General Background
In nuclear reactors, a reflector is generally placed around the core to reduce neutron leakage from the core and massive shields are utilized to protect critical areas from ionizing radiation dangerous to personnel or damaging to sensitive equipment.
Particularly in nuclear reactors designed for use in space applications, the size and mass is severely limited by mission requirements, launch vehicle limitations, and the cost of placing massive components into orbit and then assembling them into operating systems. For a small power reactor of about 100 KWe the required shield mass is about 25% of the reactor mass on an unmanned station. On manned stations or for reactors of greater power the relative mass of the shield is greater and then may become the limiting component.
Typical space reactor designs use radiation "Shadow" shields external to the reactor containment with the heat developed in the shield being dissipated by thermal radiation from the surface. The problems of neutron and gamma ray shielding are typically dealt with separately by the use of lithium hydride as the neutron shield and tungsten metal as the gamma ray shield. It can be seen from the above that there is a need for compact shield designs that minimize the overall system mass.